Life science is a roll-up of all the "wet" sciences (biology, chemistry). The Life Science skill alone cannot substitute for the Doctor or First Aid skills. Typically, Life Science challenges will require a broad range of specialized tools, that will usually be combined into an abstract "Laboratory". If a location is designated a Laboratory, please consider that it meets the prerequisites for any Life Science challenges requiring such, even if the specific tools you may need are not represented by a prop. As a skill, we expect Life Science in particular to have a great deal of effect on the campaign-wide plot. In addition, Life Science can be used to "Test for Exposure" independently of diagnosis by a Doctor.
In any given game, there may be challenges specific to that scenario. The details of that challenge will be available on the site of the challenge. Some of these may be multi-layered challenges, and those details will also be contained therein.